classes of events, they tend to retrieve a few exemplars from the relevant
classes and base their estimates on these exemplars. To illustrate, when asked if
there are more four-letter words in English that (1) begin withkor (2) havek
as their third letter, subjects consistently opt for the former alternative (which
is incorrect); presumably they do so because they can rapidly generate more
exemplars that begin withk. In studies of categorization, subjects sometimes
decide that a test item isnotaninstanceofatargetcategorybyretrievinga
counterexample; for example, subjects base their negative decision to ‘‘All birds
are eagles’’ on their rapid retrieval of the exemplar ‘‘robins’’ (Holyoak and
Glass, 1975). And if people use exemplar retrieval to make negative decisions
about category membership, they may also use exemplars as positive evidence
of category membership (see Collins and Loftus, 1975; Holyoak and Glass,
1975).
Thestudiesmentionedabovemerelyscratchthesurfaceofwhatisrapidly
becoming a substantial body of evidence for the use of exemplars in categorical
decisions (see, for example, Walker, 1975; Reber, 1976; Brooks, 1978; Medin and
Schaffer, 1978; Kossan, 1978; Reber and Allen, 1978). This body of literature
constitutes the best rationale for the exemplar view.
Concept Representations and Categorization Processes
The Critical Assumption
There is probably only one assumption that all proponents of the exemplar
view would accept: The representation of a concept consists of separate descrip-
tions of some of its exemplars (either instances or subsets). Figure 12.1 illus-
trates this assumption. In the figure the concept of bird is represented in terms
of some of its exemplars. The exemplars themselves can be represented in dif-
ferent ways, partly depending on whether they are themselves subsets (like
robin, bluejay, and sparrow) or instances (the pet canary ‘‘Fluffy’’). If the ex-
emplar is a subset, its representation can consist either of other exemplars, or
of a description of the relevant properties, or both (these possibilities are illus-
trated in figure 12.1). On the other hand, if the exemplar is an instance, it must
Figure 12.1
An exemplar representation.
278 Edward E. Smith and Douglas L. Medin